The 3GPP (3rd Generation Partnership Project) is a project that reviews and produces specifications for mobile phone systems based on evolved W-CDMA (Wideband-Code Division Multiple Access) and GSM (Global System for Mobile Communications) networks. In 3GPP, the W-CDMA scheme has been standardized as a third generation cellular mobile communication scheme, and services have been launched in succession. In addition, HSDPA (High-Speed Downlink Packet Access) with even higher communication speeds has also been standardized, and services have been launched. In 3GPP, evolutions in third generation radio access technology (Evolved Universal Terrestrial Radio Access: hereinafter referred to as E-UTRA) are being studied.
As a downlink communication scheme in E-UTRA, the OFDMA (Orthogonal Frequency Multiple Access) scheme, in which user multiplexing is performed using mutually orthogonal subcarriers, has been proposed. In addition, in the OFDMA scheme, such technologies as adaptive modulation/demodulation and error correction schemes (AMCS: Adaptive Modulation and Coding Schemes) based on such adaptive radio link control (link adaptation) as channel coding and the like are employed. AMCS refers to a scheme in which, in order to efficiently perform high-speed packet data transfer, radio transfer parameters (hereinafter referred to as AMC modes) such as error correction scheme, error correction coding rate, data modulation level, and the like are switched in accordance with the propagation channel states of each mobile station apparatus. For example, with respect to data modulation, as propagation channel states improve, by switching from QPSK (Quadrature Phase Shift Keying) modulation to multilevel modulation schemes with better modulation efficiency such as 16-QAM (Quadrature Amplitude Modulation), 64-QAM, and the like, the maximum throughput of a mobile communication system can be increased.
In OFDMA, communicable domains can be divided in the frequency domain and the time domain physically corresponding to a subcarrier. These divided domains are grouped into several resource blocks. One or a number of resource blocks are allocated to each mobile station apparatus, and communications are performed where a plurality of mobile station apparatuses are multiplexed. In order for the base station and each of the mobile station apparatuses to perform communications at optimum quality and speed suitable for their demands, it is necessary that resource blocks be allocated and transfer schemes determined taking into account the reception quality for the frequency band corresponding to each subcarrier at each mobile station apparatus and the communication speed demands of the mobile station apparatuses. Since transfer schemes and scheduling are performed by the base station apparatus, in order to realize these demands, the base station apparatus must receive feedback on reception quality from each of the mobile station apparatuses.
In addition, in E-UTRA, the use of SDM (Space Division Multiplexing) which utilizes MIMO (Multiple Input Multiple Output), or of transmit diversity, such as SFBC (Space-Frequency Block Diversity), or CDD (Cyclic Delay Diversity), has been proposed in order to increase communication channel capacity. MIMO is a collective term for multiple input multiple output systems or technologies, and is characterized in that transmission is performed by plurally branching the input and output of radio waves using a plurality of antennas on the transmitting side and the receiving side. By using MIMO, due to the multipath effect, it becomes possible to multiplex and transmit a plurality of pieces of information by forming a plurality of propagation channels as spaces, and to combine the power of the plurality of transmit antennas on the receiving side to obtain reception gain. In E-UTRA, the use of SDM based on MIMO and of transmit diversity is assumed, and the base station apparatus must determine by which scheme communications are to be performed taking into account the reception quality at the base station apparatus. In addition, with respect to when SDM is used in the downlink, preprocessing transmission signal sequences in advance (which is referred to as precoding) is being considered in order to properly separate a plurality of streams of information transmitted from the respective antennas. Precoding information is calculated based on propagation channel information that is estimated by the mobile station apparatuses, and precoding information must be feed back from the mobile station apparatuses to the base station apparatus.
Thus, in order to realize communications at optimum quality, various information must be feed back from each mobile station apparatus to the base station apparatus. The number of bits and format of this reception quality information varies depending on the granularity and quality of the information. As an example, with respect to information indicating the reception quality of downlink states for each subcarrier for optimization in the above-mentioned allocation of resource blocks, in order to allocate the most suitable frequency domain, the channel states of the respective subcarriers (frequency characteristics, that is, characteristics such as frequency-dependent transmission loss and the like) must be measured, and each channel state must be quantized and feed back to the base station apparatus (see patent document 1 indicated below). A large amount of information is required to represent this channel information, and the reception quality information must be transmitted to the base station apparatus with varying degrees of frequency in accordance with changes in the channel states.
On the other hand, when feeding back AMC modes to the base station apparatus, only a small amount of information representing the modulation scheme (64-QAM, 16-QAM, QPSK) and the coding rate (R=⅓, P=¼, and the like) is required.
In E-UTRA, the use of PUCCH (Physical Uplink Control Channel) as an uplink channel for performing this reception quality information has been considered. The PUCCH is a channel for maintaining a link in E-UTRA, and is a physical channel for multiplexing and transmitting two kinds of signals: a signal referred to as ACK/NACK, and a signal representing the reception quality information.
Of these signals, the ACK/NACK signal is a signal for notifying the base station apparatus from the mobile station apparatus whether or not the data channel transmitted in the downlink was received properly. The reception quality information is a signal for reporting downlink channel states, which is provided to the base station apparatus for controlling downlink transmission scheme.
As described above, there are various kinds of reception quality information that are transmitted from the mobile station apparatuses to the base station apparatus. Demands such as the size of the information amount transmitted, degree of frequency of transmission from the mobile station apparatus to the base station apparatus, and the like are different among one another.
In this respect, in non-patent document 1 indicated below, a proposal is made that, in transmitting the reception quality information from the mobile station apparatus to the base station apparatus, the reception quality information be transmitted using PUCCH or PUSCH (Physical Uplink Shared Channel) in accordance with service types, which have varying demands for the reception quality information. The PUSCH is a channel used for the transmission of normal data, and is a channel that is capable of transmitting larger information amounts than the PUCCH.    Patent Document 1: Japanese Patent Publication (Kokai) No. 2005-130491 A    Non-Patent Document 1: “CQI handling during DRX”, 3GPP, TSG RAN WG2 Meeting #58, R2-071901, May 2007